1. Field of the Invention
The present invention relates to a battery comprising a spirally wound body including a spirally wound laminate of a cathode and an anode with an electrolyte in between.
2. Description of the Related Art
With the recent advance of electronic technology, small and portable electronic devices such camcorders, cellular phones and laptop computers have been developed, and as power sources for the electronic devices, the development of small and lightweight secondary batteries with higher energy density has been strongly required.
Previously, secondary batteries using a graphite material which uses an intercalation reaction of lithium (Li) between graphite layers, or a carbonaceous material which uses an application of insertion/extraction reactions of lithium in pores as an anode active material have been developed, and have been put to wide practical use.
On the other hand, a demand for the capacity of the secondary batteries has further grown with a recent increase in performance of portable electronic devices. Moreover, as the portable electronic devices have become widespread, widely various demands for characteristics have been made. For example, as the operating time of devices becomes longer, the secondary batteries are required to have a higher capacity, and an improvement of cycle characteristics is strongly required so that the battery can be reused many times. Further, as the storage conditions of the batteries by users are diversified, higher performance in storage characteristics has been required.
As a battery which meets such requirements, a battery using light metal such as lithium metal as an anode active material is cited. However, in the battery, as light metal is easily deposited on an anode to form a lithium dendrite during charge, a current density becomes extremely high at an end of the dendrite, thereby the life span of the battery may be reduced due to decomposition of the electrolyte or the like, or the dendrite is excessively grown, thereby an internal short circuit in the battery may occur.
On the other hand, secondary batteries using an alloying reaction between lithium and another metal have been proposed, and among them, great expectations are placed on a secondary battery comprising an anode including silicon (Si) or tin (Sn) (for example, refer to Japanese Unexamined Patent Application Publication Nos. 2001-176545 and 2001-319696), because the battery has a large amount of lithium insertion.
However, silicon and tin each have an insertion amount of 4.4 or over lithium atoms per atom thereof, so a large change in volume of 300% to 400% occurs according to charge and discharge, and the cycle characteristics are not sufficient, therefore, a solution to this is eagerly required. A large number of improvements in performance mainly by adjustment of the composition of the anode active material have been previously proposed. Examples of an anode active material of which the composition is adjusted include an alloy including lithium, aluminum (Al) and tin (for example, refer to Japanese Unexamined Patent Application Publication No. Sho 61-66369), an alloy including tin and zinc (for example, refer to Japanese Unexamined Patent Application Publication No. Sho 62-145650), a tin alloy including 1 wt % to 55 wt % of phosphorus (P) (for example, refer to Japanese Unexamined Patent Application Publication No. Hei 8-273602), Cu2NiSn, Mg2Sn (for example, refer to Japanese Unexamined Patent Application Publication No. Hei 10-223221) and an alloy including tin and copper (for example, Japanese Unexamined Patent Application Publication No. Hei 10-308207). However, as a change in the volume of each of these anode active materials is also large, it is difficult to sufficiently improve the cycle characteristics thereof. Specifically, in a battery comprising a spirally wound laminate including a cathode and an anode, a break in the anode may occur, or a wrinkle may occur in the anode to generate a reaction active site, thereby resulting in decomposition of the electrolyte in the reaction active site.